W 21X83 vs IPE O 550
W 21X83 is an W section from the American AISC Shapes Database; IPE O 550 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 3211.9 cm³ against 3260 cm³ of plastic modulus, a difference of 1.5%. They weigh essentially the same, 123.5 kg/m and 123 kg/m. IPE O 550 is deeper, 556 mm against 543.6 mm, which matters where the floor zone is tight.
| Property | W 21X83 W | IPE O 550 IPE | Difference |
|---|---|---|---|
| Mass | 123.5 kg/m | 123 kg/m | +0.4% |
| Depth | 543.6 mm | 556 mm | -2.2% |
| Width | 212.3 mm | 212 mm | +0.1% |
| Web thickness | 13.1 mm | 12.7 mm | +3.1% |
| Flange thickness | 21.2 mm | 20.2 mm | +5.0% |
| Area | 157.4 cm² | 156 cm² | +0.9% |
| Second moment, major (Iy) | 76,170 cm⁴ | 79,200 cm⁴ | -3.8% |
| Plastic modulus, major (Wpl,y) | 3,211.9 cm³ | 3,260 cm³ | -1.5% |
| Elastic modulus, major (Wel,y) | 2,802.2 cm³ | 2,850 cm³ | -1.7% |
| Second moment, minor (Iz) | 3,388 cm⁴ | 3,220 cm⁴ | +5.2% |
| Plastic modulus, minor (Wpl,z) | 499.81 cm³ | 481 cm³ | +3.9% |
| Radius of gyration, minor (iz) | 4.65 cm | 4.55 cm | +2.2% |
| Torsion constant (It) | 180.6 cm⁴ | 187 cm⁴ | -3.4% |
W 21X83 to AISC Shapes Database v16.0; IPE O 550 to EN 10365 · Continental Steel. Difference is expressed relative to IPE O 550.
How to choose between them
On stiffness, IPE O 550 has the larger second moment of area: 79,200 cm⁴ against 76,170 cm⁴, a difference of 3.8%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram, the two are equally efficient (26.0 against 26.5 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. W sections are specified to AISC Shapes Database v16.0 and IPE to EN 10365 · Continental Steel; the steel grades, tolerances and available lengths differ, connection details and bolt gauges are set out differently, and the two are rarely both stocked in the same market. Check availability before changing a section on a drawing to save a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.